James matuison



UNITED STATES PATENT OFFICE.

A. HOEN, OF BALTIMORE, MARYLAND.

COMPOSITION FOR ETCHlNG STONE.

Specification forming part of Letters Patent No. 27,981, dated April 24,1860.

To all whom it may concern.-

Be it known that I, A. HOEN, of Baltimore, in the county of Baltimoreand State of Maryland, have invented a new and Improved Gomposition forEtching Stone; and I do hereby declare that the following is a full,clear, and

exact description of the same.

The ordinary method of etching stone is attended with many seriousdifficulties, which make it impossible to produce a perfect picture.After the stone has been prepared it is covered with an etching-groundcapable of resisting the acid to be used, (generally nitric acid orhydrochloric acid.) The design to be produced is now worked into thisground with a fine-pointed needle, the burin or graver, parallel linesbeing drawn with the ruling-machine and diamond for skies, tints, &c.The lines thus produced are all of the same size, without regard to anylight or shade, and a plate thus prepared has therefore no effectwhatever. To produce such the lines have to be etched in with nitric orhydrochloric acid, iainter or deeper, according to thelight or shade ofthe picture. For this purpose a weak solution of the acid is poured overthe whole surface of the stone, and after remaining a certain timewashed off with clean water and dried, and those parts which in theopinion of the artist are etched deep enough are stopped out withlithographic ink to prevent a further action of the acid. The acid isnow poured over the stone again and left standing long enough to producethe second tints, when the surface is washed and dried, as abovedescribed. The second tints are now stopped up, and the same process isrepeated until the several shades of the picture are produced. The mostserious defect of this process is found in the fact that the artist cannever know with certainty the depth of the lines, and he can only guessit by the strength of the acid, by the time it remains on the stone, andby the nature and chemical composition of the stone itself. Anotherdifficulty is caused by the continual stopping out of the finishedparts, which completely prevents the artist from seeing the progress ofhis picture. His memory is his only guide, and this is very apt toconfuse and mislead him. Furthermore, the gradation from one tint to theother will always be more or less visible, showing by decided marks theprevious covering with ink. All these diliiculties are avoided by theuse of my composition for producing the picture.

I prepare the stone and cover its surface with etching-ground in theusual manner. The design is now worked into the etching-ground and thestone is ready t6 be acted on by the acid, as previously described; but,instead of using nitric or hydrochloric acid for a mordant I use someacid which forms an insoluble combination with the lime of thelithographic stone-such as citric acid-which, after being washed offwith water, leaves a very small quantity of a white powder-via, citrateof lime--in the lines, which enables the artist to judge accurately oftheir respective strength by the contrast they form with the darkcovering of the stone. Such acid, however, when used alone, will spreadand run to those parts which it is not desired to touch, and in order togive to said acids a certain consistency I mix them with gum-arabic,whereby the artist is enabled to use a camels-hair brush and to put onthe acid in the same manner as if he were making an india-ink drawing.Light and shade are thus produced with equal facility and in the samemanner as with the engravers tool on copper plates previously etched, nostopping out being required until the picture is finished.

The use of gum-arabic in combination with nitric or hydrochloric acidhas been found impracticable, as it would prevent the lines from takingthe printing-ink--a fact well known to every lithographer. On the otherhand, when citric or some other acid having a similar action on thestone is used the small strata of insoluble lime left in the linesprevents the gum from sticking to the surface of the stone, and istherefore no obstacle to the lines taking ink.

The pictures taken from stones prepared according to my method bear aclose resemblance to pictures taken from copper or steel plates, and atthe same time a great many more impressions can be taken from the stonethan from the copper or steel plate, and the printin g is attended withless difficulties.

Having thus fully described my invention,

what I claim as new, and desire to secure by in the manner specified, soas to produce what Letters Patent, is I term the lithokaustik method ofetching The employment, as a mordant for lithostone. graphic stones, ofa composition ofgum-arabic, A. HOEN. or its equivalent, with citric acidor some other Witnesses: acid, forming a combination insoluble in waJAMES MATHISON, ter, with the lime of the stone, substantially W.WATKINS.

